This application claims the priority of German application No. 196 28 787.1 and PCT/EP97/03484, filed Jul. 17, 1996 and Jul. 2, 1996, respectively, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to an automatically controllable clutch between the engine and the driving wheels in the transmission line of a motor vehicle, having a transmission which can be shifted arbitrarily or manually between idling and at least one driving position, as well as having an accelerator pedal or the like for controlling the power of the engine, having a control device which controls the clutch as a function of defined parameters detected by assigned sensors. When the driving position is engaged and the accelerator pedal is not operated, the present invention has the effect that the clutch operates at its gripping point and transmits a low torque which is sufficient for a creeping of the vehicle on a level road or at a very low tractive resistance.
Motor vehicles with manually shifted gears and an automatically controlled clutch are known and are mass produced. Since, in the normal operation, the clutch as well as the transmission operate mechanically without slip, a high efficiency can be achieved; that is, corresponding systems are also suitable for comparatively low-power engines. Simultaneously, as the result of the automatic clutch, a clear increase in comfort is achieved, particularly in city stop-and-go traffic. Parking maneuvers are also facilitated in principle because, in contrast to a vehicle with a clutch which can be operated arbitrarily, for example by the pedal, the driver must not constantly "play" with the clutch.
In order to facilitate parking maneuvers and to provide the driver with a good feeling as to when and how the clutch starts to grip, British Patent No. 2 158 912 A as well as EP 0 108 315 A1 teach that, when the driving position is engaged and the accelerator pedal is not operated, the clutch already transmits a low torque which is sufficient for a creeping of the vehicle at a low tractive resistance. As soon as the driver then operates the accelerator pedal, the clutch can be controlled as a function of the torque of the vehicle engine and/or as a function of the torque which is transmitted by a shaft of the transmission line.
It is an object of the present invention to optimize, in vehicles with clutches of the initially mentioned type, the operating performance, particularly with respect to parking maneuvers.
According to the present invention, this object has been achieved by providing that, when an approximated synchronism of the clutch input and the clutch output has been reached during the phase with an engaged driving position and while the accelerator pedal is not operated, the clutch is closed when the accelerator pedal is operated while maintaining the synchronism.
The invention transmits a very slight torque to the driving wheels also when the accelerator pedal is not operated and the driving position is engaged so that the vehicle has a slight tendency to creep. This is easily possible because modern engines have a well stabilized rotational idling speed and the torque of the engine is automatically controlled for maintaining the rotational idling speed largely without delay. For the driver, the constant torque transmission to the driving wheels has the advantage that, as required, the tendency of the vehicle to creep can be slightly reduced by the service brake and can easily be increased by operating the accelerator pedal. Because the clutch constantly operates with a weak frictional connection, i.e., at its gripping point, the driver does not have to "feel out" this gripping point by operating the accelerator pedal. As a result, the vehicle acts similarly to a vehicle with a conventional automatic transmission.
By way of the characteristics according to the present invention, only a low wear of the clutch is to be advantageously expected. Consequently, even a reduction of wear may be expected because, in the case of many creeping maneuvers, a synchronism will occur within a short time between the clutch input and the clutch output and, when the accelerator pedal is now operated for accelerating the vehicle, the clutch can regularly be held in the closed condition and thus in a condition with a synchronism between the clutch input and the clutch output. When, however, the accelerator pedal is operated before the reaching of the synchronism of the clutch input and output, a particularly strong acceleration of the vehicle is achievable because the closing of the clutch takes place only at an increased rotational engine speed and an increased engine torque.